Implantable pacemakers and cardioverter defibrillators (ICDs) are available for delivering electrical stimulation therapies to a patient's heart, such as bradycardia pacing, cardiac resynchronization therapy (CRT), anti-tachycardia pacing (ATP) and cardioversion/defibrillation shocks. Pacemakers and ICDs generally sense cardiac electrical signals via electrodes coupled to the pacemaker or ICD. The cardiac electrical signals, such as an electrocardiogram (ECG) or intracardiac electrogram (EGM), are used to determine a need for electrical stimulation therapies and control the proper timing of pacing pulses based on sensed cardiac electrical signals.
Some pacemakers are implanted in a subcutaneous pocket and are coupled to transvenous leads carrying endocardial electrodes that are advanced within the heart. Advancement of medical device technology has led toward smaller and smaller implantable devices. Recently, intracardiac pacemakers have been introduced, which can be implanted directly in a heart chamber. An intracardiac pacemaker may carry electrodes directly on the housing of the pacemaker and eliminate the need for transvenous leads, which can have several advantages. For example, complications due to infection associated with a lead extending from a subcutaneous pacemaker pocket transvenously into the heart can be eliminated. Other complications, such as “Twiddler's syndrome,” are eliminated with the use of an intracardiac pacemaker.